Lymphocytes in the blood are cells that play a central role in immunity, constituting cells (subsets) having different functions, such as T cells, B cells and natural killer (NK) cells. The T cells are not a uniform group of cells but include functionally differing subsets of cells which are known as CD4 T cells, CD8 T cells or naive T cells.
The individual types of cells mentioned above have surface proteins (antigens) characteristic of the respective cell types. The number and ratio of each type of cells have conventionally been determined by dyeing a monoclonal antibody of the relevant antigen and then using a flowcytometric analysis. Also, functions of individual lymphocytes used to be determined by measuring a protein (cytokine) related to proliferative activity or proliferation of the individual lymphocytes under cultural conditions.
Using the aforementioned method, the inventors of the present Application have revealed that the subset configuration of lymphocytes and functions thereof could vary or degrade as a result of aging (refer to Non-patent Documents 1 and 2).
Non-patent Document 1: “Differential age-change in the number of CD4+, CD45RA+ and CD4+CD29+ T cell subsets in the human peripheral blood”, Mechanism of Ageing and Development, Utsuyama M., Hirokawa K., Kurashima C, Fukayama M., Inamatsu T., Suzuki K., Hashimoto W. and Sato K., Vol. 63-1, pp. 57-88, Mar. 15, 1992.
Non-patent Document 2: Katsuiku Hirokawa, “Aging and Immunity”, Nippon Ronen Igakkai Zasshi (Journal of The Japan Geriatrics Society), vol. 40-6, pp. 543-552, November. 2003.
While individual data given in these Non-patent Documents show the ratios and functions of individual cell subsets, the data do not necessarily represent the comprehensive immunity of humans.
White blood cells exist at a concentration of 4000-8000 cells/μl in peripheral blood of a healthy person. The white blood cells include (I) granular leukocytes having segmented nuclei and neutrophilic granules and (II) mononuclear cells each having a round nucleus. Most of the mononuclear cells are lymphocytes part of which constitute monocytes (macrophages) having a function of phagocytosis. The lymphocytes made of such mononuclear cells play a major role as immune cells.
The lymphocytes are made up of various subgroups having different functions. Three larger subgroups are those of T cells, B cells and NK cells.
The T cells are further divided into two large groups called CD4 T cell and CD8 T cell subsets. Either the T cells or the B cells include memory cells which have received antigenic stimulation due to infection or the like and naive cells which have not experienced any antigenic stimulation.
While the above discussion has shown a rough grouping of the lymphocytes, these groups respectively have different functions. This means that the immunity of a human is made of total capability of the functions of various subsets having such different functions.
Therefore, a subset having one function does not represent the entirety of an individual.
As explained thus far in detail, it is possible to observe the functions of a wide variety of lymphocyte subsets and proportions thereof among the entire lymphocytes. Specifically, although it is possible to acquire cell population data, such as a T cell count of 1540 cells/μl, a B cell count of 105 cells/μl and an NK cell count of 225 cells/μl, it is not obvious how individual items of these data correlate with the immunity of a human. In other words, there is a problem that no method is available to an individual person for objectively evaluating the level of his or her own immunity (immune function).